Environmental enrichment of caged animals

ABSTRACT

A cage or an item of cage furniture for use by a caged rodent comprises a coloured material which is transparent or translucent to a human observer, but is perceived as being substantially darkened or opaque by the caged rodent. The cage or item of cage furniture typically comprises, and is desirably substantially or entirely formed from, a red-coloured or red-tinted material, e.g. a synthetic plastics material. The coloured material preferably transmits less than 20% of visible light with a wavelength of less than 540 nm. The plastics material is preferably resistant to repeated autoclaving and conveniently comprises at least one of polyester, polysulfone, polytheramide and polycarbonate. Also a method of making such a cage or item of cage furniture.

FIELD OF THE INVENTION

This invention relates to a cage and an item of cage furniture forproviding environmental enrichment to a caged animal, and to a method ofmaking such a cage and such an item of cage furniture.

BACKGROUND OF THE INVENTION

Animals, especially rodents, such as mice, rats and hamsters, are oftenkept in a cage as domestic pets. It is well known to provideshelter-type objects and other items in the cage, in order to create amore stimulating environment for the animal. This is referred to asenvironmental enrichment, and the articles used in cages to provide suchenrichment are referred to generally as “cage furniture”.

As well as being kept as domestic pets, rodents are also kept in cagesfor use in research of various kinds. Conventionally, cages housinganimals for use in research purposes are substantially devoid of cagefurniture. However, there is a growing realisation that animals kept forresearch purposes should also be provided with an enriched environment,and some items of cage furniture intended for use in industrial/researchsettings are now available. It is a general object of the invention toprovide an improved cage or type of cage furniture, especially an itemof cage furniture for use in cages housing animals for use inindustrial/research settings.

SUMMARY OF THE INVENTION

In a first aspect the invention provides a cage or an item of cagefurniture for use by a caged animal, the cage or cage furniturecomprising a material which is transparent or translucent to a humanobserver, but is perceived as being substantially darkened or opaque bythe caged animal.

In embodiments of the invention in the form of a cage, the cage may beof generally conventional construction.

In embodiments of the invention in the form of an item of cagefurniture, the item conveniently takes the form of a shelter, largeenough for at least one caged animal to be accommodated therewithin,preferably large enough to accommodate two or more caged animals.

The cage or item of cage furniture in accordance with the invention istypically intended for use with one or more caged rodents, especially arat or, more preferably, a mouse, and will therefore be dimensionedaccordingly.

Preferably a cage or item of cage furniture in accordance with theinvention is substantially or entirely formed from a substance which istransparent or translucent to a human observer but substantiallydarkened or opaque to the caged animal. In preferred embodiments, thecage or the item of cage furniture is formed entirely from a syntheticplastics material, preferably by moulding, and preferably as a singlecomponent. It is also preferred that the material comprising the cage orthe cage furniture is resistant to repeated autoclaving (e.g.substantially retains its original shape and degree oftransparency/translucency to a human observer after at least 100 passesthrough an autoclave operating under normal sterilisation conditions of121° C.). Suitable commercially available plastics materials includepolyester; polysulfone, e.g. in the form of H-Temp (H-Temp is a TradeMark) from Techniplast; polytherimide, e.g. in the form of U-Temp(U-Temp is a Trade Mark) from Techniplast; and polycarbonate, e.g. inthe form of Makrolon (Makrolon is a Trade Mark).

Typically the cage or item of cage furniture will be formed from acoloured material. The colour may be an inherent property of thematerial, or the material may comprise a tinting compound or mixture toprovide the desired colour. In preferred embodiments, the cage or itemof cage furniture comprises, and is desirably substantially or entirelyformed from, a red-coloured or red-tinted material. By way ofexplanation, the inventors have observed that rodents, especially mice,are significantly less sensitive to red light than are humans.Accordingly, shelters comprising or formed from red-coloured orred-tinted materials are perceived by these animals as being ratherdark, which thus approximates more closely to the holes or nests whichmice use in their natural habitat. The inventors have discovered thatthis encourages greater use of the shelter, and behavioural activitywhich more closely follows that adopted by the animals in their naturalhabitat.

At the same time, being transparent or translucent to humans, a personworking with or looking after the caged animals, can observe the animalsat all times, even if they are inside a shelter-type item of cagefurniture. Thus, for example, a researcher can monitor the behaviour ofthe animals visually, and can count the number of animals in a cage, atany time. Thus a cage or an item of cage furniture in accordance withthe invention provides an improved degree of environmental enrichmentfor the caged animals, whilst not obstructing visual observation of theanimals within the cage or using the cage furniture.

In particular the inventors have surprisingly found that materials withparticular optical qualities are preferred for cages and/or items ofcage furniture, especially such cages or items of cage furnitureintended for rodents such as rats and, especially, mice.

In preferred embodiments, the cage or item of cage furniture comprisesor consists of a material which substantially blocks (i.e. transmitsless than 20%, preferably less than 15% of) visible light with awavelength less than 540 nm. Desirably, the material substantiallyblocks visible light with a wavelength of less than 560 nm, morepreferably less than 570 nm and most preferably 580 nm. Such materialsare commercially available and include readily available plasticsfilters, especially “cut-on” filters.

A particularly preferred material (such as a Lee polyester filter with a“cut-on” wavelength of 593 nm) substantially blocks (i.e. transmits lessthan 20% of) visible light with a wavelength of less than 580 nm, whilstbeing transparent (i.e. transmitting at least 60%) of visible light witha wavelength of 600 nm or more.

Without wishing to be bound by any particular theory, the inventorsbelieve that caged animals such as rodents prefer cages and shelters tobe darkened relative to the surrounding environment, but that the cageor shelter should not be perceived by the animals as completely dark, soas to allow some light cues to animals within the cage or shelter as tothe presence of other animals (e.g. potential predators) outside.According to this hypothesis, a preferred cage or cage furniturematerial (as represented by ‘B’ in FIGS. 3 and 4) transmits some lightof non-red or very short red wavelengths (e.g. 580–590 nm), to which theanimals are sensitive and therefore provides the animals with somevisual cues. However, the great majority of visible light wavelengths(below 580 nm), to which the animals are sensitive, are substantiallyblocked so as to provide a desirable darkening. Materials (C–E in FIGS.3–4) which do not transmit sufficient light in the 580–590 nm wavelengthrange do not give the animals sufficient light to provide the desiredvisual cues, and are therefore not so suitable, whilst other materials(e.g. A in FIGS. 3–4) transmit too much light in the 580–590 nm rangeand are not perceived by the animals as being sufficiently dark.

From the point of view of a human observer, however, material ‘B’ issubstantially transparent in the range 600 nm and above, to which thehuman eye is reasonably sensitive, so that animals within the cage oritem of cage furniture are readily visible.

For present purposes, “visible light” is intended to mean light having awavelength in the range 350–700 nm.

A preferred embodiment of cage furniture in accordance with theinvention takes the form of a substantially right-angled triangularshaped floorless shelter, which can therefore be located in a corner ofa cage, leaving a considerable free area for the animals to more aroundoutside the shelter. In addition, such a corner location tends toprevent the animals from moving the shelter (if unfixed), because thecage abuts the shelter on two sides.

If desired, the cage furniture can be provided with fixing means torestrict the movement of the cage furniture within the cage. Typicallysuch fixing means comprises a fixing member, which engages with thecage, conveniently with the roof or lid thereof. In one embodiment thefixing means comprises a chain (typically metallic) which detachablyengages with one or more bars in the lid of the cage. This arrangementallows for lifting of the cage furniture when the lid of the cage isremoved, thus enabling a person to obtain access to any of the animalsin the cage (e.g. for removal from the cage for whatever reason).

Further, a preferred embodiment of the invention will comprise at leasttwo, possibly more, entrances into the shelter.

In a second aspect the invention provides a method of making a cage oran item of cage furniture, the method comprising the step of formingsaid cage or item of cage furniture, so as to comprise a material whichis transparent or translucent to a human observer, but is perceived asbeing substantially darkened or opaque by a caged animal. Preferablyperformance of the method results in a cage or an item of cage furniturehaving one or more of the preferred features of the first aspect of theinvention as defined above.

The invention will now be further described by way of illustrativeexample and with reference to the accompanying drawings, in which:

FIG. 1 shows a prototype of an item of cage furniture in accordance withthe invention in position in a corner of a conventional animal cage;

FIG. 2 shows, to a different scale, the prototype illustrated in FIG. 1partially removed from the cage; and

FIGS. 3 and 4 are graphs of Transmission (%) against Wavelength (nm).

EXAMPLE 1

A preferred embodiment of an item of cage furniture in accordance withthe invention takes the form of a floodless shelter, formed from asingle piece of synthetic plastics material which is translucent to ahuman observer, but tinted with a red colouration. A prototype of theembodiment is shown in FIGS. 1 and 2.

With reference to FIG. 2 the shelter 10 is substantially triangular inshape, and may therefore be conveniently located in a corner of aconventional rodent cage. The shelter 10 is suitably dimensioned suchthat at least two mice or similar-sized animals can be accommodatedtherewithin.

The shelter 10 has two means of entrance/egress, a “main” entrance 12,and a “minor” entrance 14. The main entrance 12 takes the form of athree-sided short tunnel-like addition to the front face of the shelter10, which faces the space inside the cage. The minor entrance 14 isformed by a triangular-shaped raised corner portion 16 of the otherwiseflat roof 18 of the shelter 10.

The raised corner portion 16 comprises a perforation, so as to receivefixing means, which fixing means comprises a metal chain 20. The chain20 is looped around a bar in the lid of the cage, such that when the lidof the cage is raised, the shelter 10 is also lifted. The chain 20comprises a barrel-like portion, which allows two ends of the chain tobe detachably engaged in a screw-threaded engagement, such that thechain may be closed to form a loop, or opened to remove the shelter fromthe cage lid.

The flat roof 18 and the flat portion of the main entrance 12 providetwo substantially horizonal stepped surfaces, to allow, for example, forcaged animals to climb between the floor of the cage and the roof 18 ofthe shelter 10.

The shelter 10 is formed from a single piece of Makrolon polycarbonatesynthetic plastics material having a red tint. This material isresistant to repeated autoclaving washing, and is also resistant tognawing and chewing by rodents. The material is also essentiallynon-toxic to humans and rodents.

The sides of the shelter 10 are about 11.5 cm long, whereas the frontface (containing the main entrance 12) is about 16 cm long. The mainbody of the shelter 10 is about 6 cm high. The main entrance 12 forms ashort tunnel, projecting about 2 cm from the front of the shelter 10.The main entrance 12 is about 4½ cm wide and 2½ cm high.

The inventors have observed that a low entrance is just high enough topermit entrance of a normal sized mouse, and that mice prefer such a lowentrance as being similar to: their preferred natural habitats. Thewidth of the entrance is such that even pregnant female mice may stillpass freely in or out of the shelter via the main entrance. This allowsfamily groups to be housed in a single cage and permits all animals inthe group to use the cage furniture.

EXAMPLE 2

The inventors conducted a trial, comparing a shelter substantially asdescribed in Example 1 above (referred to as the “Mousehouse”), withshelters based on two other items of commercially available cagefurniture: one in the form of a substantially cylindrical, open-endedtube (the “tunnel” design) and one in the form of a substantiallybox-like shelter, with opposed sides comprising apertures formed byraised flaps (the “hangar” design). The tunnel and hangar designs asavailable commercially are of clear perspex material, and were modifiedby having a red tint applied.

Mice were placed in a cage containing one of the three items of cagefurniture, and monitored for a fixed amount of time each day. A controlgroup was also included, which comprised cages devoid of any cagefurniture. Specific types of behaviour were noted, if exhibited by themice, some behaviours being indicative of a degree of stress, otherbehaviours being similar to those observed in mice in their naturalhabitat and being indicative of a more “relaxed” state.

The method used in the trial was an application of “time budgetsampling”, a technique described by Martin and Bateson in 1986,“Measuring Behaviour: An introductory guide, CUP”. This essentiallygives a slice of an animal's behavioural repertoire at a designated timeevery day. In the present experiment this was in the dark phase, whenthe mice are most active.

The trials used 48 BALB/c mice at 7 weeks of age. The mice were dividedinto four groups by cage type as described above, including a controlgroup. Each group consisted of six male mice (held in two cages of threeanimals) and six female mice (also in two cages). Each animal wasobserved on three separate occasions and each observation was for fiveseconds per animal. This was done within a two-hour period, during thedark phase of their light cycle. These observations were done four timesin each week and the study ran for four weeks.

Data were analysed using ANOVA (Analysis of Variations) method. This isa standard procedure which compares mean scores across different groups.

Statistical significance was determined at a value of less than 0.05.The results of the trial are shown below in Table 1. In summary, animalshoused in cages containing a shelter in accordance with the inventionused the shelter far more than those housed in cages with the otheritems of cage furniture; exhibited more natural diurnal behaviour;engaged in significantly more natural self-grooming and teethmaintenance, and less running; and were generally less stressed.

The adrenal glands of the mice were also examined. The adrenal glands ofthe mice housed in cages containing a shelter in accordance with theinvention were lighter than those of other mice. Male mice, inparticular, showed a considerable difference. A lighter adrenal glandindicates that less adrenaline is being produced, suggesting a lessstressed animal.

TABLE 1 Whole-population Males-only Females-only Behaviour comparisoncomparison comparison Grooming Mousehouse mice Mousehouse miceMousehouse mice self groomed groomed groomed significantly moresignificantly more significantly more than tunnel, than tunnel mice thantunnel, Control and Control and Hangar mice Hangar mice Grooming Nosignificant No significant No significant others differences differencesdifferences Sniffing/ Mousehouse mice No significant Mousehouse miceinvestigation sniffed/ differences sniffed/ of others investigatedinvestigated others others significantly more significantly more thantunnel than tunnel, and Control mice Hangar and Control mice SniffingMousehouse mice Mousehouse mice Mousehouse mice bedding sniffed beddingsniffed bedding sniffed bedding significantly less significantly lesssignificantly less than Control mice than Control mice than Control miceSniffing Mousehouse mice Mousehouse mice Mousehouse mice bars sniffedbars sniffed bars sniffed bars significantly less significantly lesssignificantly less than tunnel, than tunnel than tunnel, Control and andControl mice Control and Hangar mice Hangar mice Sniffing Mousehousemice Mousehouse mice Mousehouse mice cage sides sniffed cage sidessniffed cage sides sniffed cage sides significantly less significantlyless significantly less than Control than Control mice than Control andtunnel mice and tunnel mice Sniffing Mousehouse mice Mousehouse mice Nosignificant through bars sniffed through sniffed through differencesbars significantly bars significantly less than Hangar less than Hangarmice mice Gnawing bars Mousehouse mice Mousehouse mice Mousehouse micegnawed bars gnawed bars gnawed bars significantly more significantlymore significantly more than tunnel than tunnel than Control mice andControl mice and Control mice Climbing/ Mousehouse mice No significantMousehouse mice holding bars climbed/held bars differences climbed/heldbars significantly less significantly less than Control mice thanControl mice Floor to bar No significant No significant No significantwheeling differences differences differences Base wheeling Nosignificant No significant No significant differences differencesdifferences Running Mousehouse mice Mousehouse mice Mousehouse micearound cage ran significantly ran significantly ran significantly lessthan tunnel less than tunnel less than tunnel and Control mice andControl mice and Control mice Jumping No significant No significant Nosignificant differences differences differences Climbing on Nosignificant No significant No significant furniture differencesdifferences differences Resting on Mousehouse mice Mousehouse miceMousehouse mice furniture rested on rested on rested on furniturefurniture furniture significantly more significantly more significantlymore than tunnel mice than tunnel mice than tunnel mice EnteringMousehouse mice Mousehouse mice Mousehouse mice furniture enteredfurniture entered furniture entered furniture significantly moresignificantly more significantly more than Hangar than Hangar thanHangar and tunnel mice and tunnel mice and tunnel mice LeavingMousehouse mice Mousehouse mice Mousehouse mice furniture left furnitureleft furniture left furniture significantly more significantly moresignificantly more than Hangar than Hangar than Hangar and tunnel miceand tunnel mice and tunnel mice

EXAMPLE 3

The aim of this trial was to determine whether, within the spectrum ofred plastics, rodents would exhibit any preference for the cagefurniture constructed at particular single wavelengths.

The inventors conducted a trial, comparing frequency of rodent use of anumber of separate shelters, each of the same size and shape (i.e. thatof the embodiment illustrated in FIG. 2).

The basic shelter was made from colourless, clear plastics material.Suitable filter materials were then applied to all the exterior surfacesof the shelters using clear, colourless adhesive (from 3M). A differentfilter was used for each shelter. The filters were supplied (fromLighting Technology, Park Royal, London) as 0.08 mm thickness sheets andcut to size, taking care that all of the shelter surface was coveredwith the chosen filter. The filters were “cut-on” filters, and possessedquoted 50% transmission levels at 614.5 nm, 610.5 nm, 602.5 nm, 593 nmand 581 nm wavelengths. The 602.5 nm filter was a “Rosco supergel”filter, made from polycarbonate. All the other filters were Lee filters,made from polyester.

The optical properties of the filters are illustrated in FIGS. 3 and 4,which are both graphs of transmission (%) against wavelength (nm).

FIG. 3 shows the transmission properties of the filters over thewavelength range 300–620 nm. The Figure shows plots of % transmissionfor the various filters as follows: (A) 581 nm filter; (B) 593 nmfilter; (C) 602.5 nm filter; (D) 610.5 nm filter; and (E) 614.5 nmfilter. As can be seen from the Figure, all of the filters substantiallyblocked (i.e. transmitted less than 20% of) all visible light ofwavelengths less than 540 nm. Light of longer wavelengths istransmitted, such that all of the filters transmitted are at least 60%of visible light with a wavelength of 620 nm or more, but each filterbad a particular wavelength (in the range 540–615 nm) above which the %transmission increased dramatically. This is shown more clearly in FIG.4, which shows the same data, but for the wavelength range 560–640 nm.Again (A)–(E) refer to one of the 5 filters used. The “cut-on”wavelengths quoted for the filters transmit 50% of incident light. The %light transmitted rapidly increases above the cut-on wavelength.

The methodology employed was derived from the first trial. The samestrain of animals was used and the same protocol followed (see Example 2above). Data were again analysed using ANOVA and findings reviewed forany significances of less than 0.05. One finding emerged at the 0.05significance level. This demonstrated that rodent use of the sheltercomprising a cut-on filter at 593 nm was significantly higher than thoseof other wavelengths.

Since all the coloured shelters were used to varying extents, and only asmall sample of possible wavelengths was trialled, the inventors cannotdemonstrate a unique rodent preference. However, the findings point toan increased preference for rodent use around the 593 nm wavelength, andmanufacture should concentrate on this area of the spectrum. Moreover,since a core advantage of the design is that it allows staff to viewanimals inside the shelter, the lighter orange/red colour of the 593 nmwavelength, is of enhanced commercial practicality.

1. At least one of a cage and an item of cage furniture for use by acaged rodent, the at least one of the cage and the item of cagefurniture comprising a coloured material which is transparent ortranslucent to a human observer, but is perceived as being substantiallydarkened or opaque by the caged rodent, wherein said coloured materialtransmits less that 20% of visible light with a wavelength of less than540 nm.
 2. At least one of a cage and an item of cage furniture for useby a caged rodent, the at least one of the cage and the item of cagefurniture comprising a coloured material which is transparent ortranslucent to a human observer, but is perceived as being substantiallydarkened or opaque by the caged rodent, wherein said coloured materialtransmits less than 20% of visible light with a wavelength of less than560 nm.
 3. At least one of a cage and an item of cage furniture for useby a caged rodent, the at least one of the cage and the item of cagefurniture comprising a coloured material which is transparent ortranslucent to a human observer, but is perceived as being substantiallydarkened or opaque by the caged rodent, wherein said coloured materialtransmits less than 20% of visible light with a wavelength of less than580 nm.
 4. At least one of a cage and an item of cage furniture for useby a caged rodent, the at least one of the cage and the item of cagefurniture comprising a coloured material which is transparent ortranslucent to a human observer, but is perceived as being substantiallydarkened or opaque by the caged rodent, wherein said coloured materialtransmits at least 60% of visible light with a wavelength of 600 nm ormore.
 5. At least one of a cage and an item of cage furniture for use bya caged rodent, the at least one of the cage and the item of cagefurniture comprising a coloured material which is transparent ortranslucent to a human observer, but is perceived as being substantiallydarkened or opaque by the caged rodent, wherein said coloured materialtransmits, on average, at least 20% of light with a wavelength in therange 580–590 nm.
 6. At least one of a cage and an item of cagefurniture according to any preceding claim, wherein said colouredmaterial is red-coloured or red-tinted.
 7. At least one of a cage and anitem of cage furniture according to claim 6, for use by a caged rat ormouse.
 8. At least one of a cage and an item of cage furniture accordingto claim 6, wherein the at least one of the cage and the item of cagefurniture is substantially or entirely formed from a substance which istransparent or translucent to a human observer but substantiallydarkened or opaque to the caged animal.
 9. At least one of a cage and anitem of cage furniture according to claim 6, wherein the at least one ofthe cage and the item of cage furniture is formed entirely from asynthetics plastics material.
 10. At least one of a cage and an item ofcage furniture according to claim 6, wherein the material comprising thecage or cage furniture is resistant to repeated autoclaving.
 11. Atleast one of a cage and an item of cage furniture according to claim 6,comprising at least one of polysulfone, polytherimide, andpolycarbonate.
 12. An item of cage furniture in accordance with claim 6,provided with fixing means to restrict the movement of the item of cagefurniture within a cage.
 13. An item of cage furniture in accordancewith claim 6, comprising at least two entrances.
 14. A method of maltingat least one of a cage and an item of cage furniture, the methodcomprising the step of forming said at least one of cage and the item ofcage furniture, so as to comprise a material which is transparent ortranslucent to a human observer, but is perceived as being substantiallydarkened or opaque by a caged rodent, and performance of which methodresults in production of the at least one of the cage and the item ofcage furniture in accordance with claim
 1. 15. A cage including an itemof cage furniture for use by a caged rodent, the item of cage furniturecomprising a coloured material which is transparent or translucent to ahuman observer, but is perceived as being substantially darkened oropaque by the caged rodent, wherein the item of cage furniture comprisesa substantially right-angled triangular shaped floorless shelter.